class_docstr: Class that enables tracking of the maximum memory utilization on a
  system.
  
  This creates a thread which samples the available memory every sample_interval_s
  seconds. The "available" memory is reported directly from psutil.
  See https://psutil.readthedocs.io/en/latest/#psutil.virtual_memory for more
  information.
code: def start(self) -> None:
      assert (
          not self._stop_event.is_set()
      ), "Can't start a thread that has been stopped."
      self._thread.start()
  
file_path: ray/release/air_tests/air_benchmarks/mlperf-train/metric_utils.py
imports: import threading
  import time
label_desc: Use image node_id 3 for calling the MaxMemoryUtilizationTracker obj's underlying member method code with example usage: obj.start() without return types